The present invention relates to a digital radio paging communication system in which a base station (or a transmitter) selectively calls a plurality of receivers, and more particularly to a digital radio paging communication system having battery saving (or low drain) receivers.
Heretofore, in such type of systems (For details, reference is made to Komura et al "New Radio Paging System" Japan Telecommunication Review, pp. 217-225, July 1977--Ref. 1), a base station repeatedly transmits a plurality of digital group signals (each group signal having a predetermined time duration and consisting of a synchronizing signal and a plurality of calling signals) On the other hand, a receiver carries out calling, battery saving, etc. in synchronism with its own synchronizing signal contained in its own digital group signal. However, the base station in such a system transmits not only the synchronizing signal but also a signal representing absence of a calling signal even when there is no need to transmit a calling signal. The base station must have a greater transmitting power accordingly. Similarly, the battery saving function of the receiver is lost during the above-mentioned predetermined time duration, regardless of whether a calling signal pertinent to the group is present or absent. This results in the increase in the power consumption at receivers.
Other prior art publications regarding the aforementioned system include the following U.S. Pat. Nos.
U.S. Pat. No. 2,884,518 issued Apr. 28, 1959--Ref. 2; PA1 U.S. Pat. No. 2,912,574 issued Nov. 10, 1959--Ref. 3; PA1 U.S. Pat. No. 3,651,413 issued Mar. 21, 1972--Ref. 4; PA1 U.S. Pat. No. 3,783,384 issued Jan. 1, 1974--Ref. 5; and PA1 Reissued U.S. Pat. No. Re. 28,222 reissued Nov. 5, 1974--Ref. 6.